Diamonds reach the Earth's surface carried within specific volcanic eruptions originating deep within the planet.
Diamonds form under extreme pressure and temperature conditions found hundreds of kilometers below the surface, primarily in the Earth's mantle. They are not formed in the surface crust. Getting them from these depths to the surface requires a very specific geological process.
The Journey from Mantle to Surface
Based on geological evidence, including the provided reference, the primary mechanism for bringing diamonds to the surface is through rare volcanic activity.
Diamonds are brought to the surface from the mantle in a rare type of magma called kimberlite and erupted at a rare type of volcanic vent called a diatreme or pipe.
Here's a breakdown of this process:
- Origin in the Mantle: Diamonds crystallize deep within the Earth's mantle, typically at depths ranging from 150 to 200 kilometers (about 90-125 miles).
- Transporting Magma (Kimberlite): A special type of magma, known as kimberlite, originates even deeper within the mantle. This magma is rich in volatile compounds (like carbon dioxide and water) and ascends rapidly towards the surface. Kimberlite acts as a 'lift' for diamonds, carrying them along on its turbulent journey.
- Rapid Ascent: The rapid ascent of kimberlite is crucial. If the journey were slow, the diamonds would likely turn back into graphite under the decreasing pressure and increasing temperature nearer the surface. The speed helps preserve the diamond structure.
- Eruption (Diatreme/Pipe): Kimberlite magma doesn't typically form large, cone-shaped volcanoes like those seen with basaltic lava flows. Instead, it erupts through narrow, carrot-shaped volcanic pipes, known as diatremes or kimberlite pipes. These are the primary source rocks where diamonds are found close to the surface.
Key Characteristics of Diamond-Bearing Eruptions
- Rarity: Both kimberlite magma and the diatreme eruption style are geologically rare events. This is why diamond deposits are not widespread globally.
- Speed: The extremely fast ascent rate of kimberlite magma prevents diamonds from degrading during their journey to the surface.
- Location: Kimberlite pipes are found in stable, old continental crust areas called cratons, which have thick roots extending deep into the diamond-stability zone of the mantle.
Essentially, diamonds hitch a ride on a very specific, rare, and fast-moving elevator system from the deep mantle to the Earth's surface, powered by kimberlite volcanism.
